Liquid-vapor interfacial properties of vibrating square well chains.

Liquid-vapor interfacial properties of square well chains are calculated. Surface tension, orthobaric densities, and vapor pressures are reported. Spinodal decomposition with a discontinuous molecular dynamics simulation program is used to obtain the results which are compared to previously published data for orthobaric densities and vapor pressures. In order to analyze the effect of the chain stiffness results for near tangent and overlapping linear chains as well as angled chains are obtained. Properties are calculated for linear chains of 2, 4, and 8 spheres for intramolecular distances of 0.97, 0.6, and 0.4 as well as for angled chains of 4 and 8 spheres and intramolecular distances of 0.4. The complete series of fully flexible near tangent square well chains is also studied (chains of 2, 4, 8, 12, and 16 particles with intramolecular distances of 0.97). The corresponding states principle applies to most of the systems considered. Critical properties values are reported as obtained from orthobaric densities, surface tensions, and vapor pressures. For the near tangent chains the critical temperatures increase with chain length but the rate of increment tends to zero for the longest chains considered. When the stiffness of the chain increases (intramolecular distance from 1 , 0.6, and 0.4) this saturation effect is either not present or reverses itself. The surface tension increases with the length of the chain while the width of the interface decreases.